Radios commonly include oscillators to generate sinusoidal signals used to perform up-conversion and down-conversion from base band to carrier frequency and back, respectively. Sinusoidal signals may be characterized by their frequency, amplitude and phase. The oscillator is relied upon to generate a reliable frequency and phase. It has been observed that oscillators tend to generate non-ideal sinusoidal signals, but instead signals with a partially random phase variation over time, commonly referred to as phase noise (PN).
FIG. 1 illustrates graphs, over a 100 microsecond duration, of phase variation in baseband for four different mmWave radio devices. As may be observed, the different devices exhibit very distinct phase drift characteristics.
The phase variations may constitute a dominating impairment for high throughput wireless communications systems operating at high carrier frequencies. The phase variations, if not accounted for correctly, may deteriorate signal quality measures at all parts of the receiver signal processing chain. For instance, the channel estimation quality may be less accurate. Another example is a residual phase rotation of a constellation diagram after equalization at the receiver as shown in FIGS. 2 and 3 for two different radio devices using a binary phase shift keying (BPSK) modulation scheme.
As 5G wireless systems are expected to operate at higher carrier frequencies as compared to 4G wireless systems, this problem can be considered to become a dominating impairment which needs to be carefully accounted for algorithmically at a wireless receiver.